From the Guidelines
Thyroid nodules should be biopsied based on their size, ultrasound characteristics, and patient risk factors, with fine needle aspiration (FNA) biopsy generally recommended for nodules ≥1 cm with suspicious ultrasound features. The decision to perform a biopsy on a thyroid nodule should consider several factors, including the nodule's size, ultrasound characteristics, and patient risk factors, as outlined in the studies 1, 2, 3.
Key Considerations
- Nodules ≥1 cm with suspicious ultrasound features, such as irregular margins, microcalcifications, hypoechogenicity, or a taller-than-wide shape, should be biopsied.
- Nodules <1 cm may also require biopsy if there are clinical or ultrasonographic suspicions of malignancy, such as a history of head and neck irradiation, family history of thyroid cancer, or presence of cervical adenopathy.
- Purely cystic nodules rarely require biopsy, as they are unlikely to be malignant.
- Patient risk factors, such as history of radiation exposure, family history of thyroid cancer, or concerning symptoms like hoarseness or lymphadenopathy, may lower the threshold for biopsy.
- TSH levels should also be considered, as elevated TSH slightly increases cancer risk.
Diagnostic Approach
- Fine needle aspiration cytology (FNAC) is a sensitive and specific diagnostic tool for differentiating between benign and malignant nodules, although it has limitations, such as inadequate samples and follicular neoplasia 2.
- In cases of inadequate samples, FNAC should be repeated, while follicular neoplasia with normal TSH and a "cold" appearance on thyroid scan may require surgical consideration.
- Measurement of serum calcitonin is a reliable tool for diagnosing medullary thyroid cancer and should be an integral part of the diagnostic evaluation of thyroid nodules 1.
Management
- The initial treatment of differentiated thyroid carcinoma (DTC) should always be preceded by careful exploration of the neck by ultrasound to assess the status of lymph node chains 2.
- Total or near-total thyroidectomy is generally recommended for DTC, with less extensive surgical procedures considered for small, intrathyroidal tumors with favorable histological types.
- Prophylactic central node dissection is controversial, but may be considered in cases with preoperative suspicion or intraoperative proof of lymph node metastases.
From the Research
Indications for Biopsy
- Thyroid nodules with suspicious ultrasonography findings, such as hypoechogenicity, irregular margins, absence of halo, taller-than-wide shape, increased vascularity, and microcalcifications, should be considered for biopsy, regardless of cytological results 4
- Nodules larger than 1 cm should be biopsied, especially if they have features suggestive of malignancy or if the patient has risk factors for thyroid cancer 5
- The American Association of Clinical Endocrinologists guidelines recommend biopsying hypoechoic nodules with at least one additional suspicious feature, such as irregular margins, length greater than width, and microcalcifications 6
Ultrasound Patterns and Biopsy
- The 2015 American Thyroid Association (ATA) guidelines provide a classification system for ultrasound patterns, which can help identify nodules with a high suspicion of malignancy 7
- Nodules with very low or low suspicion of malignancy on ultrasound can be followed up with ultrasound, while those with intermediate or high suspicion should be evaluated with repeat fine-needle aspiration biopsy 7
- The TIRADS classification system can help identify subcentimeter nodules that should be biopsied, with higher classifications (4A, 4B, 4C, and 5) indicating a higher risk of malignancy 8